My gun is leaking! Help!

Alright I have a tippmann 98c platimun with the act. I have had it since christmas and used it only 3 times. A few weeks ago I got a double trigger and installed it. I tested it out and i noticed a quiet leaking sound coming out from the gun. The sound is coming out like an inch above where the hose connects into the gun. I hoped it wasent too serious. 3 days ago, i went paintballing all day and the gun worked fine, but lost my co2 really fast. (my 20 oz went down in like an hour and only played like 4 rounds). So the leak is definatly a problem. Just about an hour ago, i dissasembled it and tried to find the problem. I had it mostly assembled and the leak is coming from where the hose goes into the black metal thing. (sorry not sure what its called). im not sure how to fix this! I tried tightning the hose and it seemed to make almost worse. So does anyone have advice for me on how to fix this? Maybe i have to take apart that black bolt metal part where the hose conencts to? please help!!!

the air line in the platinumis a pressure line. the line screwes into a nut in the body which presses againts the valve. you cant use teflon tape or anything. the best way is to make sure there is no obstructions on the line and valve, no burs or anything. then make sure the line is seated up against the valve correcly, not twisted or anything. then tighten it good.  DO NOT over tighten! if it still leaks a little, try to tighten it a little more.